Simultaneous Yb³⁺-Induced Phase Transition and Sensitized Luminescence in Er³⁺-Doped KNN-Based Lead-Free Ceramics for Optical Thermometry

Abstract

Environment-friendly potassium sodium niobate-based ferroelectrics have been widely and deeply studied for their electrical properties, but there remains much potential for applications in other fields, one of which is in optical temperature sensing. Herein, a host (K,Na)­Li0.04NbO3:0.5 mol% Er material with an orthogonal–tetragonal phase transition was constructed by Li+ regulation and then increased Yb2O3 codoping used to promote the occurrence of orthogonal to tetragonal and tetragonal to pseudocubic phase transitions. Interestingly, codoping with Yb2O3 as a sensitizer and phase structural changes regulated the resulting materials’ luminescent characteristics and greatly enhanced luminescence intensity and temperature sensing properties, compared with those of merely Er3+-doped samples. In addition, strong green and red light emissions were related to the large absorption cross-section of Yb3+ near 980 nm, which transferred more energy to Er3+. In particular, significantly enhanced red light, or red shift, was associated with energy back transfer at high Yb3+ concentrations. Furthermore, the optimal ceramic was (K, Na)­Li0.04NbO3:0.5 mol % Er/2.5 mol % Yb (KNL0.04N:0.5 Er/2.5 Yb), and its maximum absolute and relative sensitivity of 0.0112 and 0.0173 K–1, respectively, which were higher than those of other reports. These results showed that KNL0.04N:0.5Er/2.5Yb lead-free ceramic possessed the potential to be an excellent optical temperature sensor with high intensity and sensitivity.

A Review on Optical Applications, Prospects, and Challenges of Rare-Earth Oxides

“…The addition of 0.5% Er 2 O 3 significantly improved the ferro- and piezoelectric properties (i.e., due to the doping impact of the donor) of the ceramic synthesis and resulted in an intense photoluminescence. Additionally, the codoping of Er 3+ with Yb 2 O 3 greatly improved the upconversion intensity of the (K,Na)­Li 0.04 NbO 3 host material (as demonstrated in Figure and Figure ) when compared with only Er 3+ -doped samples …”

“…Additionally, the codoping of Er 3+ with Yb 2 O 3 greatly improved the upconversion intensity of the (K,Na)Li 0.04 NbO 3 host material (as demonstrated in Figure 15 and Figure 16) when compared with only Er 3+ -doped samples. 124 In a different study, the Mg-borate glass properties were found to be sensitive to Dy 3+ concentrations. 125 The 0.7% Dy 3+ was hypersensitive at 1260 nm.…”

“…(a) Upconversion spectrum of Yb y /0.5Er:KNL x N ( x = 0.04; y = 0–5), (b) red-green emission intensity at different doping concentrations, (c, e) upconversion intensity at different wavelengths, and (d, f) logarithmic intensity vs logarithmic power at different wavelengths. Reproduced from ref . Copyright 2020 American Chemical Society.…”

“…(a) Upconversion luminescence mechanism of Yb y /0.5Er:KNL x N ( x = 0.04; y = 0–5) and (b) upconversion flowcharts of green and red lights. Reproduced from ref . Copyright 2020 American Chemical Society.…”